Laminated metal sheet is a composite of a thin viscoelastic polymer layer sandwiched between outer layers of metal sheet. Typically the overall thickness of the laminated sheet is not greatly dissimilar to the thickness of a solid monolithic sheet. Hence laminated sheet may comprise metal sheets each ranging in thickness from 0.5 to 1 millimeter, with a viscoelastic core which may be as thin as 3 micrometers thick, but more commonly is about 50 micrometers thick. This thin viscoelastic layer is effective in providing sound and vibration damping. Thus, laminated steel finds application in automobile passenger cabins where it can reduce noise and vibration while offering advantages over more traditional approaches to noise reduction such as mastic, spray-on deadener, matting etc. In many cases, the metal sheets are steel, but the product is not restricted to specific metal sheet materials or alloys or grades of a specified material.
These laminated metal sheets are broadly compatible with the manufacturing processes employed for sheet metal panels but they also exhibit some unique characteristics. For example, the coefficient of thermal expansion of the viscoelastic core is substantially higher than that of any candidate metallic surface. Thus, when subject to thermal excursions, differences in the magnitude of the thermal expansion or contraction will lead to the development of interfacial stresses and possibly global deformation of the laminate. This behavior will be more pronounced if a temperature differential exists through the laminate thickness since this will give rise to differential stresses at the interfaces between the metal sheets and the viscoelastic layer. Also, viscoelastic materials are not electrical conductors. Hence without addition of conductive material to the viscoelastic core, conventional spot welding, the traditional joining method of choice for automobile bodies, is rendered difficult or impossible.
These characteristics impose additional design and manufacturing constraints and must be accommodated by users in applying laminated metal sheet. Thus, there are opportunities to broaden the utility of laminated metal sheet and more particularly, laminated steel sheet, by eliminating or reducing the manufacturing and/or in-use impacts of these characteristics.